Graphene is a newly realized two-dimensional (2D) electron system
that has attracted a great deal of interest in the scientific community because of the new physics which it exhibits and because of
its potential as a new material for electronic technology [1]}, [2]}. The agent responsible for many of
the interesting electronic properties of graphene sheets is the non-Bravais honeycomb-lattice
arrangement of Carbon atoms, which leads to a gapless semiconductor
with valence and conduction \(\pi \) -bands.
States near the Fermi energy of a graphene sheet are described by a spin-independent massless Dirac Hamiltonian [3]}
\({\cal H}_{\rm D} = v_{\rm F} {\sigma }\cdot {p}~,\) 
